17O NMR study of the inhomogeneous electronic state in La2-xSrxCuO4 crystals

We report measurements on the inhomogeneous line broadening of the O-17 NMR spectrum in the high T-c superconductor La2-xSrxCuO4 for single crystals with nominal hole concentrations x=0.035, 0.05, 0.07, 0.115, and 0.15. A substantial overlap between the O-17 NMR spectrum of different crystals is reported, and the extent of the overlap is shown to increase with decreasing temperature. The spin-lattice relaxation rate divided by temperature, 1/(T1T)-T-17, is found to vary linearly with frequency (or Knight shift K-17(spin), equivalently) across the O-17 NMR spectrum of each crystal, with the same scaling form given by 1/(T1T)-T-17=beta K-17(spin), where beta=2.4(2) (sK%)(-1). We therefore argue that the overlap between the O-17 NMR spectrum of different crystals x is a result of an inherent spatial variation in hole concentration within each crystal, and that the extent of the line broadening, (17)Delta K-spin, is a measure of the extent (17)Delta x(local) (or amplitude) of the spatial variation in local hole concentration, (17)x(local)=x +/-(17)Delta x(local). We successfully fit the O-17 NMR line shapes with a simple numerical model that determines the random distribution in local hole concentration (17)x(local) as a result of the random spatial distribution in Sr2+ hole donors within a patch radius R-17(patch). We find that R-17(patch)=2-5 nm best fits the data, implying a short length scale for the inhomogeneous electronic state. In this report we present the first systematic study of the spatial distribution in the local static spin susceptibility in the high T-c cuprates.